Ka/Ks Ratio Calculator

Ka/Ks ratio (ω) indicates the type of selection: ω < 1 suggests purifying selection (harmful mutations removed), ω = 1 indicates neutral evolution, and ω > 1 suggests positive selection (beneficial mutations favored). See also our Molecular Clock Calculator.

Ka is the rate of nonsynonymous substitutions that change amino acids, while Ks is the rate of synonymous substitutions that don't change amino acids. Their ratio helps measure selection pressure on protein function.

Nei-Gojobori (1986) is the most widely used and standard method. Li-Wu-Luo is good for closely related sequences, while Modified Nei-Gojobori corrects for multiple substitutions at the same site.

Input sequences should be protein-coding DNA sequences in FASTA format or raw nucleotide sequences. The sequences must be properly aligned and of the same length for accurate calculations. You might also find our Selection Coefficient Calculator useful.

A Ka/Ks ratio near 1 suggests neutral evolution where both synonymous and nonsynonymous mutations are equally tolerated, indicating relaxed selection pressure on the protein.

This calculator is specifically designed for protein-coding sequences. Non-coding regions don't have synonymous and nonsynonymous sites, so Ka/Ks analysis is not applicable to them.

Ka/Ks > 1 indicates positive selection, where nonsynonymous changes are favored over synonymous ones. This suggests the protein is evolving under selective pressure for functional changes.

Yes, it's recommended to remove positions with gaps as they can introduce artifacts in the calculation. Gaps represent insertions/deletions rather than substitutions and should be excluded from Ka/Ks analysis.